How does solar permitting work in the City of Phoenix?

The City of Phoenix Building Services Division handles solar permits. Phoenix participates in SolarAPP+ for qualifying residential solar systems under 15 kW. For standard residential systems, Phoenix processes solar permits through the Phoenix Permits portal. Commercial systems require full plan review. Phoenix has one of the highest solar permit volumes in the US due to the excellent desert climate and strong solar market.

What is the conductor derating for Phoenix solar installations?

Phoenix has the highest effective conductor temperature of any major US solar market. ASHRAE maximum air temperature: 43°C. Adding the NEC 310.15(B)(3)(c) 22°C rooftop adder: effective conductor temperature = 65°C. Temperature correction factor for THWN-2 (90°C conductors): 0.65. This means Phoenix conductors must be sized at (Isc × 1.25) ÷ 0.65 minimum — significantly larger than in cooler markets.

How does APS solar interconnection work?

Arizona Public Service (APS) serves most of the Phoenix metro area. APS requires solar interconnection applications through their online portal. Residential systems under 10 kW use APS's simplified residential interconnection process. APS's net metering program (Resource Comparison Proxy, or RCP) credits excess solar at the avoided cost rate — APS does not offer full retail-rate net metering. The RCP rate is lower than retail but consistent.

How does SRP solar interconnection work?

Salt River Project (SRP) serves parts of the eastern Phoenix metro (Tempe, Mesa, Chandler, Scottsdale, Gilbert areas). SRP's E-27 price plan applies to new solar customers — SRP does not offer traditional net metering. SRP's E-27 includes a solar access charge and credits excess production at a rate determined by SRP's pricing schedule. SRP's solar program is different from APS and less favorable for simple residential solar economics.

Does Phoenix have a property tax exemption for solar?

Arizona provides a property tax exemption for residential solar energy devices under Arizona Revised Statutes § 42-11054. The full value added to a home by a residential solar installation is exempt from property tax assessment. Commercial solar is also eligible for favorable property tax treatment. This exemption applies statewide including Phoenix and Maricopa County.

Phoenix Solar Permit Guide 2026: City of Phoenix Permits, APS Interconnection & Desert Climate Derating

Phoenix is the single largest US solar market by installed residential capacity, driven by the best solar irradiance in the continental US and high electricity rates. The desert climate creates engineering challenges — Phoenix conductor derating is more aggressive than any other major US city — but the solar resource makes the economics compelling.

Phoenix Solar Snapshot

NEC Edition: 2020 | Utilities: APS (west Phoenix metro) + SRP (east valley) | APS Net Metering: Resource Comparison Proxy (RCP) rate — not full retail | SRP Solar: E-27 plan with solar access charge | Property Tax: Solar devices fully exempt | Federal ITC: 30% residential / up to 50% commercial

Phoenix Desert Climate Engineering

Phoenix presents the most aggressive conductor derating scenario in US solar:

Conductor Ampacity in Phoenix

Conductor	NEC Table 310.16 (90°C)	Phoenix Derated (0.65)
14 AWG	25A	16.3A
12 AWG	30A	19.5A
10 AWG	40A	26.0A
8 AWG	55A	35.8A
6 AWG	75A	48.8A

Critical: Terminal Temperature Rating

The 75°C terminal limitation is most consequential in Phoenix:

Conductor	90°C Column	75°C Column (terminal-limited)
10 AWG	40A	35A
8 AWG	55A	50A
6 AWG	75A	65A

Example: 12 AWG derated for Phoenix: 30A × 0.65 = 19.5A. If inverter terminals rated 75°C: 25A × 0.65 = 16.3A. A single string at 9.58A Isc: required = 9.58 × 1.25 / 0.65 = 18.42A. If using 75°C column: 16.3A < 18.42A — fails. Need 10 AWG for Phoenix if inverter terminals are 75°C-rated.

Phoenix NEC 690.7 String Voltage

Phoenix T_min = 2°C:

For Voc = 45.0V, β_Voc = -0.28%/°C:

Factor = 1 + (2 - 25) × (-0.0028) = 1 + 0.0644 = 1.0644
Max modules (600V) = 600 / (45.0 × 1.0644) = 12.52 → 12 modules
Max modules (1000V commercial) = 1000 / (45.0 × 1.0644) = 20.87 → 20 modules

APS Interconnection

Arizona Public Service serves the central and western Phoenix metro (Phoenix, Glendale, Peoria, Avondale, Goodyear, Surprise, Scottsdale west of Hayden Rd):

APS Process

System Size	Track	Timeline
Under 10 kW residential	Simplified	10–20 business days
10 kW–2 MW	Level 1 study	45–90 days
Over 2 MW	Level 2 study	6–18 months

APS Net Metering (Resource Comparison Proxy)

APS’s net metering uses the Resource Comparison Proxy (RCP) rate, not full retail:

RCP rate: approximately $0.09–0.12/kWh (varies quarterly)
Retail rate: approximately $0.14–0.17/kWh (varies by tier and TOU)
Monthly excess credits at RCP rate
Annual excess: paid at RCP rate

APS’s RCP rate is lower than retail but is still a defined and consistent credit. The economics are less favorable than states with full retail net metering but better than states with pure avoided cost credits.

SRP Interconnection

Salt River Project serves eastern Phoenix metro (Mesa, Tempe, Chandler, Gilbert, Scottsdale east, Ahwatukee, parts of Phoenix):

SRP E-27 Solar Plan

SRP’s solar customers are placed on the E-27 Price Plan:

Monthly solar access charge (~$32–50/month depending on system size)
Time-of-use rates apply to all electricity consumption
Solar generation credits applied at a defined rate
Different economics than APS — monthly fixed charge affects small system ROI

SRP vs. APS: Very Different Economics

SRP’s E-27 solar plan includes a monthly solar access charge ($32–50/month) plus time-of-use pricing. For small residential systems, the fixed monthly charge can significantly offset solar savings. Before designing a system in SRP territory, model the full E-27 economics including the solar access charge — the solar economics differ substantially from APS territory even for the same solar resource.

City of Phoenix Permit Process

SolarAPP+ Track (Residential, under 15 kW)

Phoenix participates in SolarAPP+:

Submit through SolarAPP+-compatible design software
Automated approval — typically same-day
Apply for Phoenix permit with SolarAPP+ certificate
Phoenix issues permit
Install + inspection
APS/SRP interconnection activation

Standard Track

Submit through Phoenix Permits online portal
Submit electrical one-line, structural plan, equipment specs
Plan review: 5–15 business days
Permit issued
Install
Schedule Phoenix Building Services inspection
Utility interconnection

Phoenix Permit Fees

System	Approximate Fee
Residential SolarAPP+	~$100–200
Standard residential	~$150–400
Commercial	Valuation-based

Maricopa County (Unincorporated)

Maricopa County Building Services serves unincorporated areas of the county:

Separate from City of Phoenix
County solar permit process
SolarAPP+ participation varies — confirm with Maricopa County
Many suburban Phoenix areas (parts of Scottsdale, Mesa, Chandler, Gilbert) are incorporated cities with their own permits — not County

Phoenix-Ready Solar Permit Packages with Desert Derating

SurgePV applies Phoenix ASHRAE data (43°C max, effective 65°C rooftop) automatically and generates NEC 2020-compliant permit packages formatted for Phoenix Building Services, APS, and SRP interconnection.

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Frequently Asked Questions

What is the conductor derating for Phoenix solar?

Phoenix has the highest effective rooftop temperature in the US: 43°C air + 22°C adder = 65°C effective. THWN-2 correction factor: 0.65. Required conductor ampacity = (Isc × 1.25) ÷ 0.65. If inverter terminals are 75°C-rated, use the 75°C ampacity column — this often requires the next larger conductor size vs. the 90°C calculation.

What is the difference between APS and SRP for solar?

APS credits excess solar at the Resource Comparison Proxy (RCP) rate (~$0.09–0.12/kWh). SRP places solar customers on the E-27 plan with a monthly solar access charge ($32–50/month) — this monthly fixed charge affects ROI for small systems. Determining which utility serves the project address is the first step in any Phoenix solar project.

Does Phoenix use SolarAPP+?

Yes — City of Phoenix participates in SolarAPP+ for residential systems under 15 kW. Maricopa County (unincorporated) and other Phoenix metro cities (Mesa, Chandler, etc.) have separate permitting processes.